1. Field of the Invention
The present invention relates to an apparatus and method for interference cancellation in a multi-antenna system. More particularly, the present invention relates to an apparatus and method for canceling interference between multiple users and for suppressing interfering signals from neighboring cells in a multi-antenna system of a multi-cell multi-user environment.
2. Description of the Related Art
With the rapid growth of wireless mobile communication markets, demand for a variety of multimedia services has been dramatically increasing. Thus, progress is being made in the providing of a large capacity of communication systems and the transmission of data at a high speed in order to provide such large-sized multimedia services. Also, recent information theoretical researched on a multi-antenna system has shown that a Multiple Input Multiple Output (MIMO) system enables to efficiently use a limited frequency.
Compared to a single-antenna system, a multi-antenna system can provide greater transmission reliability and a higher transmission rate without additional usage of frequency resource or transmission power by transmitting data over each antenna.
The multi-user multi-antenna system can also provide a greater spectral efficiency by allowing multiple users to simultaneously share spatial resources secured through the multiple antennas.
In a multi-user multi-antenna system, a transmitting end precodes and transmits a signal to each user in order to avoid generating interference between the users. For example, the transmitting end may employ a linear scheme such as a Zero Forcing (ZF) technique, a Minimum Mean Square Error (MMSE) technique, or a Block Diagonalization (BD) technique in order to reduce interference between multiple users. For another example, the transmitting end can employ a Dirty Paper Coding (DPC) technique or a Tomlinson Harashima preceding scheme to satisfy a system channel capacity while reducing signal interference between multiple users.
As mentioned above, the transmitting end precodes a signal to cancel interference between users located in the same cell, and transmits the signal to target users. Accordingly, from the transmitting end, the users receive a signal from which interference between the users located in the same cell has been canceled. The signal received by the users can be expressed by Equation 1 below:
                                                                        y                k                            =                                                                    H                    k                                    ⁢                                      M                    k                                    ⁢                                      s                    k                                                  +                                                      H                    k                                    ⁢                                                            ∑                                                                        l                          =                          1                                                ,                                                  l                          ≠                          k                                                                    K                                        ⁢                                                                                  ⁢                                                                  M                        l                                            ⁢                                              s                        l                                                                                            +                                                      H                                          I                      ,                      k                                                        ⁢                                      x                                          I                      ,                      k                                                                      +                                  n                  k                                                                                                        =                                                                    H                    k                                    ⁢                                      x                    k                                                  +                                                      H                    k                                    ⁢                                                            ∑                                                                        l                          =                          1                                                ,                                                  l                          ≠                          k                                                                    K                                        ⁢                                                                                  ⁢                                          x                      l                                                                      +                                  z                  k                                                                                        (        1        )            
In equation 1, yk denotes a signal received by a kth user, Hk denotes a channel between a transmitting end and the kth user, Mk denotes a precode for canceling interference between users within the same cell in the transmitting end, sk denotes a signal transmitted by the transmitting end, and xk denotes a signal precoded and transmitted by the transmitting end. Ml denotes a precode for other users within the same cell, sl denotes a signal transmitted to other users from the transmitting end, and xl denotes a signal precoded and transmitted by the transmitting end. HI,k denotes channels of neighbor cells, xI,k denotes interference signals of the neighbor cells, and nk denotes a white noise of the kth user. Here, zk represents HI,kxI,k+nk.
As in Equation 1, the transmitting end of the multi-antenna system can precode a transmitted signal and reduce interference between users within the same cell.
However, there is a problem of increased interference from adjacent cells that degrade a throughput performance of communication system even though the transmitting end performs preceding to reduce interference between users within the same cell.